1. Field of the Invention
The present invention relates to a clamp apparatus capable of clamping a workpiece by the aid of an arm which is rotatable by a predetermined angle in accordance with a driving action of a driving mechanism.
2. Description of the Related Art
Conventionally, for example, when a constitutive part of an automobile or the like is welded, a clamp cylinder has been used in order to clamp the constitutive part. Such a clamp cylinder is disclosed, for example, in U.S. Pat. No. 4,458,889.
As shown in FIGS. 8 and 9, in the clamp cylinder disclosed in U.S. Pat. No. 4,458,889, a piston rod 2, which is movable back and forth in accordance with a driving action of a cylinder 1c, is arranged between a pair of divided bodies 1a, 1b. A coupling 3 is connected to a first end of the piston rod 2. A pair of links 5a, 5b and a pair of rollers 6a, 6b are rotatably installed to both sides of the coupling 3 respectively by the aid of a first shaft 4. An arm 8, which is rotatable by a predetermined angle, is connected between the pair of links 5a, 5b by the aid of a second shaft 7.
In this case, the pair of rollers 6a, 6b are provided slidably by the aid of a plurality of needles 9a which are installed to holes. The piston rod 2 is provided displaceably integrally with the rollers 6a, 6b in accordance with a guiding action of the rollers 6a, 6b which are slidable along track grooves 9b formed on the bodies 1a, 1b respectively.
However, in the case of the clamp cylinder disclosed in U.S. Pat. No. 4,458,889 concerning the conventional technique described above, for example, when the arm 8 is in an unclamping state in which an unillustrated workpiece is not held and when the supply of the pressure fluid to the cylinder 1c is cut off due to any cause, then the arm 8 is in a free state, because the transmission of the driving force to the arm disappears. It is feared that the arm 8 may be spontaneously rotated, for example, due to the force of inertia of the arm 8 or the operation of a robot or the like to which the clamp cylinder is installed.
In view of the above, it is conceived that the unclamping state of the arm 8 is held by means of the frictional force based on the sliding resistance of a piston which is slidable along a cylinder chamber, or the unclamping state of the arm 8 is held by increasing the frictional force by means of the sliding resistance of a link mechanism. However, the following inconvenience arises. That is, the frictional resistance is changed by the abrasion of the sliding portion due to the use of the clamp cylinder for a long period of time. It is impossible to reliably maintain the unclamping state of the arm 8.
A general object of the present invention is to provide a clamp apparatus which makes it possible to reliably hold an arm in an unclamping state even when transmission of driving force to the arm is cut off.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.